1. Field of the Invention
The present invention relates to a wiring substrate on which a wiring portion is formed.
2. Description of the Related Art
For example, in an electrode for a plasma display panel (PDP), a silver electrode (hereinafter, referred to as Ag wiring portion) and a gold electrode (hereinafter, referred to as Au wiring portion) are connected to each other, for the purpose of suppressing migration of silver.
However, diffusion occurred in an interface between the Au wiring portion and the Ag wiring portion. More or less, diffusion necessarily occurs in an interface between the wiring portions having different materials. In addition, silver is more easily diffused in comparison with gold. In other words, since silver has a significantly large diffusion coefficient, silver was diffused into the Au wiring portion and thus a void was generated in the Ag wiring portion. Accordingly, for example, when the wiring portion is formed and plating is performed on the surface of the wiring portion, it may be difficult to perform the plating at a place where the void is generated. In a worst case, disconnection may occur.
In addition, the diffusion may also occur between the Ag wiring portion and a substrate. In particular, when low temperature co-fired ceramic (LTCC) is used for the substrate, Ag was apt to be diffused into the substrate and thus the above-described problems have occurred.